NIR spectroscopy applied to fruits and vegetables

NIR spectroscopy applied to fruits and vegetables

NIR spectroscopy applied to fruits and vegetables

NIR spectroscopy applied to fruits and vegetables

NIR spectroscopy applied to fruits and vegetables

Near infrared spectroscopy (NIR), which covers approximately 780 to 2500 nm, has many applications in the fruit and vegetables industry, and can be used to measure moisture, soluble solids content, water content, stiffness or presence of internal damage, among other parameters. In this post, the use of NIR spectroscopy for the measurement of different attributes in fruits and vegetables is reviewed.

 

When radiation falls on a sample, it can be reflected, absorbed or transmitted (see our previous post), and the contribution of each phenomenon depends on the chemical composition and physical parameters of the sample.

 

Interaction light-sample. NIR spectroscopy applied to fruits and vegetables

 

The reflected light (either by specular or diffuse reflection) provides information about the surface of the sample. Scattering (the dispersion of light) is the result of the refractions that occur inside the sample when the phase changes (and therefore the refractive index), being the cell walls the main elements that produce scattering in fruits and vegetables. Scattering also occurs due to the presence of suspended particles such as starch grains, chloroplasts and mitochondria, and depends on the size, shape and microstructure of the particles. Finally, scattering can also appear due to the presence of discontinuities in the sample, such as pores, openings or capillaries. Scattering affects the intensity more than the shape of the reflected spectrum.

 

Absorption determines the shape of the reflected spectrum. The absorption bands depend on the chemical composition of the sample. In the case of fruits and vegetables, the absorption peaks associated with the OH bonds of the water, as well as the C-H and N-H bonds, are the most characteristic ones.

 

One of the most common applications of NIR spectroscopy in the case of fruits and vegetables is the measurement of the content in Brix degrees, that is, the percentage of its content in soluble solids, a parameter related to maturity. Soluble solids include sugars (major component, 80%), salts, acids, and other water-soluble components. Many studies to measure Brix degrees have been carried out with different varieties of apples, but there are also studies with other fruits, such as peach, pear, melon or pineapple. The determination of previous parameters usually requires the combination of NIR and visible (380-780 nm) spectroscopy measurements.

 

Fruits and vegetables. NIR spectroscopy.

 

Other attributes measured in fruits and vegetables with NIR spectroscopy include dry matter (content of the sample, in mass or percentage, excluding water), pH or acidity. The dry matter content is a relevant parameter that is used to establish the ripening of certain fruits and can affect their taste or nutritional status. In the case of dry matter, good calibration models are obtained with NIR, while it is more difficult to accurately predict the degree of acidity.

 

Good results are also obtained with spectroscopy to predict attributes related to texture, such as firmness or the presence of surface defects. In the latter case, it is common to use multispectral techniques (working with a few wavelengths) and hyperspectral (using a continuum of wavelengths). Finally, NIR spectroscopy is also used for variety discrimination or the detection of contaminants or infections.

 

In conclusion, NIR spectroscopy allows measuring quality parameters in fruits and vegetables quickly, easily and continuously, providing benefit to the agri-food industry. In order to develop reliable calibration models it must be considered that a large number of samples covering all the variations for which the model should work (different varieties, seasons, origin) must be evaluated.

 

Learn more about Pyroistech’s solutions for industry based on spectroscopy

 

Related articles:

NIR spectroscopy applied to the wine industry

NIR spectroscopy applied to meat

 

Bibliography

 

[1] Nicolaï, B.M.; Beullens, K.; Bobelyn, E.; Peirs, A.; Saeys, W.; Theron, K.I.; Lammertyn, J. Nondestructive measurement of fruit and vegetable quality by means of NIR spectroscopy: A review. Postharvest Biol. Technol. 2007, 46, 99–118, doi:10.1016/J.POSTHARVBIO.2007.06.024.

 

[2] Peiris, K.H.S.; Dull, G.G.; Leffler, R.G.; Kays, S.J. Spatial Variability of Soluble Solids or Dry-matter Content within Individual Fruits, Bulbs, or Tubers: Implications for the Development and Use of NIR Spectrometric Techniques. HortScience 1999, 34, 114–118, doi:10.21273/HORTSCI.34.1.114.

 

[3] Wang, H.; Peng, J.; Xie, C.; Bao, Y.; He, Y. Fruit Quality Evaluation Using Spectroscopy Technology: A Review. Sensors 2015, 15, 11889–11927, doi:10.3390/s150511889.

 

[4] Chandrasekaran, I.; Panigrahi, S.S.; Ravikanth, L.; Singh, C.B. Potential of Near-Infrared (NIR) Spectroscopy and Hyperspectral Imaging for Quality and Safety Assessment of Fruits: an Overview., doi:10.1007/s12161-019-01609-1.

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